What is the ruling on a woman's fasting if her menstrual cycle is irregular, where her period of purity ranges between 15 and 26 days, and her period of menstruation is between 7 and 8 days?

As long as the period of cessation of menstruation is fifteen days, then whatever is seen after this period is considered menstruation. This is because the minimum period of purity between two menstruations, according to the majority of scholars, is fifteen days, and according to the Hanbalis, it is thirteen days. If blood is seen at a time when it is possible for it to be menstruation, then it is considered menstruation, even if it differs from the usual time.